The present invention relates to internal combustion engines and particularly, but not exclusively, to internal combustion engines for model aircraft.
At present model aircraft use internal combustion engines comprising a reciprocating piston disposed within a cylinder where the energy created by the explosion of an air/fuel mixture within the cylinder causes the piston to reciprocate in a linear motion. This linear motion is converted to a rotational motion by a transmission unit. Such designs comprise a cylinder disposed transversely of the propeller shaft and which is difficult to contain within the body shell of the aircraft. In fact, no attempt is usually made to enclose the projecting cylinder.
EP-A-0016381 discloses an internal combustion engine in which the cylinder and the transmission are carried by the housing and the output is taken off the crankshaft.
According to a first aspect of the invention there is provided an internal combustion engine comprising an outer housing, a rotatable cylinder disposed within the housing, valve means to provide a communication with the cylinder space for gaseous material, a reciprocable piston disposed coaxially witi the cylinder, and a power transmission means, characterized in that a substantially linear movement of the piston is substantially converted by the transmission means into a rotational movement of the cylinder, the said cylinder comprising a rotational output drive means, the said transmission means comprising a connecting rod connecting the piston to a crank shaft and a gearing connecting the crank shaft to the cylinder.
Preferably, the cylinder is formed with at least one port providing communication with the cylinder space.
Preferably the outer housing is formed with an inlet port and an outlet exhaust port.
Preferably the outlet exhaust port extends for substantially one quarter of the circumference of the outer housing.
Preferably the outer housing is formed with a port to receive an electrical glow plug or spark plug.
It is preferable that an electrical battery is used to power the glow plug during the initial start up of the internal combustion engine. Preferably the glow plug retains sufficient heat energy from the combustion of the air/fuel mixture to aid the combustion of the subsequent air/fuel mixture. Alternatively, the battery is used to aid the subsequent combustion of the air/fuel mixture following initial start up.
Preferably the internal combustion engine is a four stroke engine.
Preferably the valve means operates by rotational indexing of the cylinder port relative to the outer housing ports.
Preferably the valve means also operates by rotational indexing of the cylinder port relative to the port receiving the glow plug. It is preferable that the indexing takes place when the compression ratio within the cylinder is at an optimum level.
It will be appreciated that the glow plug is exposed to the air/fuel mixture within the cylinder only when the cylinder port is indexed to a position adjacent to the said glow plug.
In conventional glow plug combustion engines the glow plug is permanently in contact with the air/fuel mixture in the cylinder during compression and the explosion occurs when the air/fuel mixture reaches a certain compression. The level of compression is limited to this explosion compression for a specific air/fuel mixture and glow plug temperature. It will be appreciated that the present invention is not limited by the explosion compression as the glow plug is not permanently exposed to the air/fuel mixture. The explosion occurs when the glow plug is exposed to the mixture.
Preferably the output drive means is disposed coaxially with respect to the cylinder.
Preferably the outer housing comprises a circular radially outer securing ring and a circular radially inner timing ring.
Preferably the output drive means comprises a shaft fixed to the axially outermost end of the cylinder.
Preferably the output drive means comprises a propeller detachably fixed coaxially on the shaft.
Preferably the transmission means comprises a connecting shaft suitably fixed to the piston, a crank pin, a crankshaft disposed substantially perpendicular to the axis of the piston; a drive gear wheel disposed coaxially on the crankshaft and meshing with a driven gear wheel disposed coaxially at one end of the cylinder, the arrangement being such that, in use, the drive gear wheel has a rotational speed twice that of the driven gear wheel.
The 2:1 drive ratio provides appropriate valve timing for a four-stroke engine.
Preferably the connecting shaft is fixed to the piston by a gudgeon pin.
Preferably the cylinder and piston are made from cast iron or steel. It will be appreciated that the sliding contact between the cylinder and the piston provides a sufficient gas tight seal which withstands the compression ratio provided by the internal combustion engine and the pressures produced within the combustion engine in use.
Alternatively, the cylinder is made from brass and comprises a hard chrome coating on its internal surface, and the piston is made from an aluminium alloy.
Alternatively, the connecting shaft is fixed to the piston by a universal ball and socket joint such that, in use, the piston is rotatable at substantially the same angular velocity as the rotating cylinder, and preferably the piston then comprises at least one piston ring disposed coaxially thereon.
Preferably the outer securing ring is made from an aluminium alloy. Also preferably the inner timing ring is made from a steel alloy.
Preferably the propeller provides, in use, an axial force, and the axial force is substantially transferred to the outer housing via the cylinder.
According to a second aspect of the invention, there is provided an internal combustion engine in accordance with the said first aspect of the invention, wherein said rotatable cylinder is a combustion cylinder, comprising a seal assembly for sealing a port in said rotatable combustion cylinder disposed for rotation within said outer housing, the seal assembly comprising a circular seal ring adapted to be disposed within a circular recess extending radially through the wall of the combustion cylinder, and a resilient means adapted, in use, to urge the circular seal ring in a radially outward direction, with respect to the rotational axis of the cylinder, towards an inner surface of the outer housing so providing, in use, a substantially gas tight seal between an inner chamber of the combustion cylinder and atmosphere.
Preferably the circular seal ring has an outer surface comprising a radius of curvature substantially equal to the radius of the radially inner surface of the outer housing.
Preferably the resilient means comprises a circular resilient ring of substantially circular cross section. Alternatively, the resilient ring comprises a substantially rectangular cross-section.
Preferably the circular recess is a circular stepped recess.
Preferably the circular seal ring comprises a body portion directed towards the cylinder axis; the radial depth of the body portion being substantially less than the radial depth of the stepped recess and being in sliding contact therewith; and a tube portion depending from the body portion and being of a thickness substantially less than the body portion and being in sliding contact with the wall of the stepped recess.
Preferably the resilient ring is housed in the stepped recess.
It is preferable that the circular seal ring is made from a phosphor bronze material. Alternatively, the circular seal ring is made from a cast iron material.
Preferably the resilient ring is made from Viton(trademark). Alternatively, the resilient ring is made from a silicone rubber material.
Preferably the internal combustion engine is suitable for and intended for use with a model aircraft.
According to a third aspect of the invention there is provided a method of converting energy from an explosion or burning of a fuel or an air/fuel mixture in an engine in accordance with said first or second aspect of the invention, comprising substantially converting the explosive energy into a linear movement of the piston; converting the linear movement of the piston into a rotational movement of the cylinder and taking the output drive from the rotating cylinder to provide an output drive means.
Preferably the output drive means comprises a propeller detachably fixed coaxially on the shaft wherein the output drive from the cylinder is used to rotate the propeller to create forward thrust.
Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: